Inhibition of fibrinolysis by lipoprotein(a)

Inverse Association of Lipoprotein(a) on Long-Term Bleeding Risk in Patients with Coronary Heart Disease: Insight from a Multicenter Cohort in Asia

BACKGROUND

 Lipoprotein(a), or Lp(a), has been recognized as a strong risk factor for atherosclerotic cardiovascular disease. However, the relationship between Lp(a) and bleeding remains indistinct, especially in the secondary prevention population of coronary artery disease (CAD). This investigation aimed to evaluate the association of Lp(a) with long-term bleeding among patients with CAD.

METHODS

 Based on a prospective multicenter cohort of patients with CAD consecutively enrolled from January 2015 to May 2019 in China, the current analysis included 16,150 participants. Thus, according to Lp(a) quintiles, all subjects were divided into five groups. The primary endpoint was bleeding at 2-year follow-up, and the secondary endpoint was major bleeding at 2-year follow-up.

RESULTS

 A total of 2,747 (17.0%) bleeding and 525 (3.3%) major bleeding were recorded during a median follow-up of 2.0 years. Kaplan-Meier survival analysis showed the highest bleeding incidence in Lp(a) quintile 1, compared with patients in Lp(a) quintiles 2 to 5 (p < 0.001), while the incidence of major bleeding seemed similar between the two groups. Moreover, restricted cubic spline analysis suggested that there was an L-shaped association between Lp(a) and 2-year bleeding after adjustment for potential confounding factors, whereas there was no significant association between Lp(a) and 2-year major bleeding.

CONCLUSION

 There was an inverse and L-shaped association of Lp(a) with bleeding at 2-year follow-up in patients with CAD. More attention and effort should be made to increase the clinician awareness of Lp(a)'s role, as a novel marker for bleeding risk to better guide shared-decision making in clinical practice.

The effect of tibolone treatment on apolipoproteins and lipoprotein (a) concentrations in postmenopausal women: A meta-analysis of randomized controlled trials

OBJECTIVE

Tibolone is a synthetic steroid with estrogenic, androgenic and progestogenic properties that is used as hormone replacement therapy (HRT) in postmenopausal women. Treatment with tibolone has been demonstrated to lead to changes of the lipid profile, including alterations in lipoprotein (a) and apolipoprotein levels. Hence, we conducted the present meta-analysis of randomized controlled trials (RCTs) to assess the effect of tibolone treatment on apolipoproteins and lipoprotein (a) values in postmenopausal women.

METHODS

Several databases (Cochrane Library, PubMed/Medline, Scopus, and Google Scholar) were searched for English-language manuscripts published up to September 2023 that scrutinized the effects of tibolone administration on apolipoprotein A-I (ApoA-I), apolipoprotein A-II (ApoA-II), apolipoprotein B (ApoB), and lipoprotein (a) in postmenopausal women. The results were reported as the weighted mean difference (WMD) with a 95% confidence interval (CI), generated using a random-effects model.

RESULTS

Finally, 12 publications with 13 RCT arms were included in the current meta-analysis. The overall results from the random-effects model demonstrated a notable reduction in ApoA-I (n = 9 RCT arms, WMD: -34.96 mg/dL, 95 % CI: -42.44, -27.48, P < 0.001) and lipoprotein (a) (n = 12 RCT arms, WMD: -7.49 mg/dl, 95 % CI: -12.17, -2.81, P = 0.002) after tibolone administration in postmenopausal women. However, treatment with tibolone did not impact ApoA- II (n = 4 RCT arms, WMD: 1.32 mg/dL, 95 % CI: -4.39, 7.05, P = 0.64) and ApoB (n = 9 RCT arms, WMD: -2.68 mg/dL, 95 % CI: -20.98, 15.61, P = 0.77) values. In the subgroup analyses, we noticed a notable decrease in lipoprotein (a) levels when tibolone was prescribed to females aged < 60 years (WMD: -10.78 mg/dl) and when it was prescribed for ≤ 6 months (WMD: -15.69 mg/dl).

CONCLUSION

The present meta-analysis of RCTs highlighted that treatment with tibolone reduces lipoprotein (a) and apolipoprotein A-I levels in postmenopausal women. As the decrease in serum lipids' concentrations is associated with a decrease in the risk of cardiovascular disease (CVD), treatment with tibolone could be a suitable therapy for postmenopausal women with elevated CVD risk.

Association of Lipoprotein(a) Levels With Myocardial Fibrosis in the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Lipoprotein(a) (Lp[a]) has been identified as an emerging risk factor for adverse cardiovascular (CV) outcomes, including heart failure. However, the connections among Lp(a), myocardial fibrosis (interstitial and replacement), and cardiac remodeling as pathways to CV diseases remains unclear.

OBJECTIVES

This study investigated the relationship between Lp(a) levels and myocardial fibrosis by cardiac magnetic resonance (CMR) T1 mapping and late gadolinium enhancement, as well as cardiac remodeling by cine CMR, in the MESA (Multi-Ethnic Study of Atherosclerosis) cohort.

METHODS

The study included 2,040 participants with baseline Lp(a) measurements and T1 mapping for interstitial myocardial fibrosis (IMF) evaluation in 2010. Lp(a) was analyzed as a continuous variable (per log unit) and using clinical cutoff values of 30 and 50 mg/dL. Multivariate linear and logistic regression were used to assess the associations of Lp(a) with CMR measures of extracellular volume (ECV fraction [ECV%]), native T1 time, and myocardial scar, as well as parameters of cardiac remodeling, in 2,826 participants.

RESULTS

Higher Lp(a) levels were associated with increased ECV% (per log-unit Lp[a]; β = 0.2%; P = 0.007) and native T1 time (per log-unit Lp[a]; β = 4%; P < 0.001). Similar relationships were observed between elevated Lp(a) levels and a higher risk of clinically significant IMF defined by prognostic thresholds per log-unit Lp(a) of ECV% (OR: 1.20; 95% CI: 1.04-1.43) and native T1 (OR: 1.2; 95% CI: 1.1-1.4) equal to 30% and 955 ms, respectively. Clinically used Lp(a) cutoffs (30 and 50 mg/dL) were associated with greater prevalence of myocardial scar (OR: 1.85; 95% CI: 1.1-3.2 and OR: 1.9; 95% CI: 1.1-3.4, respectively). Finally, higher Lp(a) levels were associated with left atrial enlargement and dysfunction.

CONCLUSIONS

Elevated Lp(a) levels are linked to greater subclinical IMF, increased myocardial scar prevalence, and left atrial remodeling.

Association between lipoprotein(a) and ischemic stroke: Fibrinogen as a mediator

BACKGROUND

Previous studies have reported lipoprotein(a) was related to increased risk of ischemic stroke. However, the role of fibrinogen in their associations was not fully elucidated.

AIM

We aimed to investigate the mediating role of fibrinogen in the association between lipoprotein(a) and risk of ischemic stroke.

METHODS

A total of 516 patients with ischemic stroke were matched 1:1 to patients without ischemic stroke for age and gender. Serum lipoprotein(a) and plasma fibrinogen levels were collected on the basis of the results of biochemical tests. Multivariate conditional logistic regression analyses were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for lipoprotein(a) levels and ischemic stroke risk. Mediation analysis were further conducted to evaluate the potential mediating role of fibrinogen in the association between lipoprotein(a) and ischemic stroke risk.

RESULTS

The lipoprotein(a) level of subjects with ischemic stroke was significantly higher than that of subjects without ischemic stroke (P < 0.001). Each SD increment of lipoprotein(a) was associated with 27% higher odds (OR 1.27, 95%CI: 1.11, 1.45) increment in ORs of ischemic stroke. Furthermore, mediation analyses indicated that fibrinogen mediated 10.15% of the associations between lipoprotein(a) and ischemic stroke.

CONCLUSIONS

Higher level of lipoprotein(a) was independently associated with increased risk of ischemic stroke and fibrinogen partially mediated the associations of lipoprotein(a) and ischemic stroke risk.

Thrombosis associated with mycoplasma pneumoniae infection (Review)

Mycoplasma pneumoniae is a common pathogen causing respiratory infections in children and adults. In addition to respiratory diseases, Mycoplasma pneumoniae is also involved in numerous extrapulmonary diseases. Thrombosis is an extrapulmonary manifestation associated with Mycoplasma pneumoniae infection. In recent years, an increasing number of case reports have been published identifying thrombosis secondary to Mycoplasma pneumoniae infection. In the present study, the available relevant literature in English available on PubMed, Medline and Web of Science was consulted. The results of the present study demonstrated that in patients with thrombosis caused by Mycoplasma pneumoniae infection, some of the factors causing thrombosis are transient and some are due to hereditary thrombophilia. Following timely treatment, the majority of patients recovered completely but some patients had a poor prognosis. The present review focuses on the pathogenesis, clinical features, treatment and prognosis of this crucial issue, which contributes toward the understanding of the disease.

Lipoprotein(a) and Cardiovascular Disease Prevention across Diverse Populations

Lipoprotein(a) (Lp(a)) is a highly proatherogenic lipid fraction that is genetically determined and minimally responsive to lifestyle or behavior changes. Mendelian randomization studies have suggested a causal link between elevated Lp(a) and heart disease, stroke, and aortic stenosis. There is substantial inter-ethnic variation in Lp(a) levels, with persons of African descent having the highest median values. Monitoring of Lp(a) has historically been limited by lack of standardization of assays. With the advent of novel therapeutic modalities to lower Lp(a) levels including proprotein convertase subtilisin/kexin 9 (PCSK9) inhibitors and targeted antisense oligonucleotides, it is increasingly important to screen patients who have family or personal history of atherosclerotic cardiovascular disease for elevations in Lp(a). Further study is needed to establish a causal relationship between elevated Lp(a) and cardiovascular disease across diverse ethnic populations.

Elevated Lp(a) (Lipoprotein[a]) Levels Increase Risk of 30-Day Major Adverse Cardiovascular Events in Patients Following Carotid Endarterectomy

Background and Purpose:

General population studies have shown that elevated Lp(a) (lipoprotein[a]) levels are an emerging risk factor for cardiovascular disease and subsequent cardiovascular events. The role of Lp(a) for the risk of secondary MACE in patients undergoing carotid endarterectomy (CEA) is unknown. Our objective is to assess the association of elevated Lp(a) levels with the risk of secondary MACE in patients undergoing CEA.

Methods:

Lp(a) concentrations were determined in preoperative blood samples of 944 consecutive patients with CEA included in the Athero-Express Biobank Study. During 3-year follow-up, major adverse cardiovascular events (MACE), consisting of myocardial infarction, stroke, and cardiovascular death, were documented.

Results:

After 3 years follow-up, Kaplan-Meier cumulative event rates for MACE were 15.4% in patients with high Lp(a) levels (>137 nmol/L; >80th cohort percentile) and 10.2% in patients with low Lp(a) levels (≤137 nmol/L; ≤80th cohort percentile; log-rank test: P =0.047). Cox regression analyses adjusted for conventional cardiovascular risk factors revealed a significant association between high Lp(a) levels and 3-year MACE with an adjusted hazard ratio of 1.69 (95% CI, 1.07–2.66). One-third of MACE occurred within 30 days after CEA, with an adjusted hazard ratio for the 30-day risk of MACE of 2.05 (95% CI, 1.01–4.17). Kaplan-Meier curves from time point 30 days to 3 years onward revealed no significant association between high Lp(a) levels and MACE. Lp(a) levels were not associated with histological carotid plaque characteristics.

Conclusions:

High Lp(a) levels (>137 nmol/L; >80th cohort percentile) are associated with an increased risk of 30-day MACE after CEA. This identifies elevated Lp(a) levels as a new potential risk factor for secondary cardiovascular events in patients after carotid surgery. Future studies are required to investigate whether Lp(a) levels might be useful in guiding treatment algorithms for carotid intervention.

Hyperlipoproteinemia (a) is associated with breast cancer in a Han Chinese population

To investigate the relationship between serum lipoprotein (a) (LP(a)) levels and breast cancer as well as the clinicopathologic characteristics of breast cancer in a Han Chinese population.This study included 314 breast cancer patients, 51 patients with benign breast tumors, and 185 healthy control subjects. All study subjects were Han Chinese with similar socio-economic backgrounds, who were local residents of Zhoushan, Zhejiang, China or who had lived in Zhoushan for a long period of time. Serum concentrations of LP(a) were determined using a latex-enhanced immunoturbidimetric assay. Clinicopathological characteristics of patients were retrieved from medical records, which included the histopathological type, grade, stage, and molecular subtype of the disease, the expression of estrogen receptor (ER), progesterone receptor (PR), HER2, and Ki67, and the level of reproductive hormones. Correlations between 2 groups were evaluated using the Spearman correlation analysis. Associations among ≥3 groups were interpreted using the Kruskal-Wallis H test or the logistic regression test.Elevated serum LP(a) levels were detected in breast cancer patients compared with healthy control subjects, but no significant differences in LP(a) were detected between breast cancer and benign tumor or between benign tumor and healthy control. In breast cancer patients, serum LP(a) levels were inversely associated with HER2 expression, but they were not significantly correlated with any other clinicopathologic characteristics of breast cancer evaluated in this study.Elevated serum LP(a) levels were associated with breast cancer in a Han Chinese population.

Identification and analyses of inhibitors targeting apolipoprotein(a) kringle domains KIV-7, KIV-10, and KV provide insight into kringle domain function

Increased plasma concentrations of lipoprotein(a) (Lp(a)) are associated with an increased risk for cardiovascular disease. Lp(a) is composed of apolipoprotein(a) (apo(a)) covalently bound to apolipoprotein B of low-density lipoprotein (LDL). Many of apo(a)'s potential pathological properties, such as inhibition of plasmin generation, have been attributed to its main structural domains, the kringles, and have been proposed to be mediated by their lysine-binding sites. However, available small-molecule inhibitors, such as lysine analogs, bind unselectively to kringle domains and are therefore unsuitable for functional characterization of specific kringle domains. Here, we discovered small molecules that specifically bind to the apo(a) kringle domains KIV-7, KIV-10, and KV. Chemical synthesis yielded compound AZ-05, which bound to KIV-10 with a K_d of 0.8 μm and exhibited more than 100-fold selectivity for KIV-10, compared with the other kringle domains tested, including plasminogen kringle 1. To better understand and further improve ligand selectivity, we determined the crystal structures of KIV-7, KIV-10, and KV in complex with small-molecule ligands at 1.6-2.1 Å resolutions. Furthermore, we used these small molecules as chemical probes to characterize the roles of the different apo(a) kringle domains in in vitro assays. These assays revealed the assembly of Lp(a) from apo(a) and LDL, as well as potential pathophysiological mechanisms of Lp(a), including (i) binding to fibrin, (ii) stimulation of smooth-muscle cell proliferation, and (iii) stimulation of LDL uptake into differentiated monocytes. Our results indicate that a small-molecule inhibitor targeting the lysine-binding site of KIV-10 can combat the pathophysiological effects of Lp(a).

Lipoprotein(a) the Insurgent: A New Insight into the Structure, Function, Metabolism, Pathogenicity, and Medications Affecting Lipoprotein(a) Molecule

Lipoprotein(a) [Lp(a)], aka "Lp little a", was discovered in the 1960s in the lab of the Norwegian physician Kåre Berg. Since then, we have greatly improved our knowledge of lipids and cardiovascular disease (CVD). Lp(a) is an enigmatic class of lipoprotein that is exclusively formed in the liver and comprises two main components, a single copy of apolipoprotein (apo) B-100 (apo-B100) tethered to a single copy of a protein denoted as apolipoprotein(a) apo(a). Plasma levels of Lp(a) increase soon after birth to a steady concentration within a few months of life. In adults, Lp(a) levels range widely from <2 to 2500 mg/L. Evidence that elevated Lp(a) levels >300 mg/L contribute to CVD is significant. The improvement of isoform-independent assays, together with the insight from epidemiologic studies, meta-analyses, genome-wide association studies, and Mendelian randomization studies, has established Lp(a) as the single most common independent genetically inherited causal risk factor for CVD. This breakthrough elevated Lp(a) from a biomarker of atherosclerotic risk to a target of therapy. With the emergence of promising second-generation antisense therapy, we hope that we can answer the question of whether Lp(a) is ready for prime-time clinic use. In this review, we present an update on the metabolism, pathophysiology, and current/future medical interventions for high levels of Lp(a).

Serum lipoprotein(a) and risk of hemorrhagic stroke among incident peritoneal dialysis patients: a large study from a single center in China

Background: This retrospective study investigated whether baseline serum lipoprotein(a) (Lp(a)) may predict subsequent stroke in patients under chronic peritoneal dialysis (PD). Methods: Eight hundred and sixty incident PD patients, treated from 1 November 2005 to 28 February 2017, were enrolled, and followed until discontinuation of PD, death, or 31 May 2017. Hemorrhagic or ischemic stroke was the primary outcome. The population was stratified by baseline serum Lp(a) tertile. The risk of each stroke subtype was analyzed using the Cox proportional hazard models. Adjustments were made for: age; gender; history of stroke and hypertension; systolic blood pressure; lipid-lowering, antiplatelet and antihypertensive medications; laboratory profiles including hemoglobin, serum albumin, calcium, triglyceride, total and low-density lipoprotein cholesterol; and apolipoprotein A1. Results: Among the 860 participants, 19.3% and 4.1% had diabetes mellitus and a history of stroke, respectively. The median baseline serum Lp(a) was 328 (172-585) mg/L. After 28 (14-41) months of follow-up, 33 (3.84%) and 12 (1.40%) patients developed hemorrhagic and ischemic stroke, respectively. Participants in the highest Lp(a) tertile had a significantly lower risk of hemorrhagic stroke compared with those in the lowest tertile (hazard ratio (HR) 0.3, 95% confidence interval (CI) 0.1-0.86; p = .026); the rates of ischemic stroke were comparable among the tertiles. Each 10 mg/L rise in serum Lp(a) was associated with a 2% (95% CI 0.96-1; p = .033) lower risk of hemorrhagic stroke. Conclusions: Among patients with incident PD, a higher serum Lp(a) level may predict a lower risk of hemorrhagic stroke.

Lipoprotein(a) plasma levels, bone mineral density and risk of hip fracture: a post hoc analysis of the Women's Health Initiative, USA

OBJECTIVES

Elevated Lipoprotein(a) (Lp[a]) is a well-known risk factor for cardiovascular disease. However, its roles in bone metabolism and fracture risk are unclear. We therefore investigated whether plasma Lp(a) levels were associated with bone mineral density (BMD) and incident hip fractures in a large cohort of postmenopausal women.

DESIGN

Post hoc analysis of data from the Women's Health Initiative (WHI), USA.

SETTING

40 clinical centres in the USA.

PARTICIPANTS

The current analytical cohort consisted of 9698 white, postmenopausal women enrolled in the WHI, a national prospective study investigating determinants of chronic diseases including heart disease, breast and colorectal cancers and osteoporotic fractures among postmenopausal women. Recruitment for WHI took place from 1 October 1993 to 31 December 1998.

EXPOSURES

Plasma Lp(a) levels were measured at baseline.

OUTCOME MEASURES

Incident hip fractures were ascertained annually and confirmed by medical records with follow-up through 29 August 2014. BMD at the femoral neck was measured by dual X-ray absorptiometry in a subset of participants at baseline.

STATISTICAL ANALYSES

Cox proportional hazards and logistic regression models were used to evaluate associations of quartiles of plasma Lp(a) levels with hip fracture events and hip BMD T-score, respectively.

RESULTS

During a mean follow-up of 13.8 years, 454 incident cases of hip fracture were observed. In analyses adjusting for confounding variables including age, body mass index, history of hysterectomy, smoking, physical activity, diabetes mellitus, general health status, cardiovascular disease, use of menopausal hormone therapy, use of bisphosphonates, calcitonin or selective-oestrogen receptor modulators, baseline dietary and supplemental calcium and vitamin D intake and history of fracture, no significant association of plasma Lp(a) levels with low hip BMD T-score or hip fracture risk was detected.

CONCLUSIONS

These findings suggest that plasma Lp(a) levels are not related to hip BMD T-score or hip fracture events in postmenopausal women.

TRIAL REGISTRATION NUMBER

NCT00000611; Post-results.

Elevated lipoprotein(a) as a new risk factor of cerebral venous sinus thrombosis: association with fibrin clot properties

Elevated lipoprotein(a) [Lp(a)] has been reported to be associated with prothrombotic clot phenotype. We hypothesized that increased Lp(a) contributes to cerebral venous sinus thrombosis (CVST) and its recurrence in relation to clot features. In 80 consecutive patients (aged 39.36 ± 10.18 years, 61 women) following the first CVST after anticoagulation withdrawal, we assessed Lp(a) levels and plasma clot properties. Recurrence of CVST was recorded during follow-up (median 53, interquartile range 40-59 months). Lp(a) levels were inversely associated with clot permeability (K_s, r = - 0.58, P < 0.001) and the rate of D-dimer release from clots in the presence of tissue plasminogen activator (r = - 0.27, P = 0.017) along with increased maximum absorbance of fibrin gels (r = 0.42, P < 0.001) and maximum D-dimer levels achieved during lysis (D-D_max, r = 0.29, P = 0.01). Recurrence of CVST was observed in 12 patients (15%) after median follow-up of 26 months. Lp(a) concentrations were higher in patients with recurrence of CVST compared to the remainder (14.15 [8.85-25.25] vs. 28.3 [18.9-35.6] mg/dL; P = 0.001). The risk of recurrent CVST was fourfold higher among 17 (21.25%) patients with Lp(a) > 30 mg/dL compared to the remainder (adjusted hazard ratio, 3.9; 95% confidence interval [CI] 1.23-12.4). Recurrence of CVST was associated with 14% lower K_s (P = 0.001) and 10% higher D-D_max (P = 0.008), with no differences in other clot features. Multiple logistic regression model showed that CVST recurrence was independently associated with Lp(a) (odds ratio 1.09, 95% CI 1.02-1.16). Increased Lp(a) characterizes subjects at elevated risk of recurrent CVST after anticoagulation withdrawal, which could be partly explained by formation of denser fibrin clots.

High Lipoprotein(a) and Low Risk of Major Bleeding in Brain and Airways in the General Population: a Mendelian Randomization Study

BACKGROUND

The physiological role of lipoprotein(a) is unclear; however, lipoprotein(a) may play a role in hemostasis and wound healing. We tested the hypothesis that high lipoprotein(a) concentrations are associated with low risk of major bleeding in the brain and airways both observationally and causally (from human genetics).

METHODS

We examined 109169 individuals from the Copenhagen City Heart Study and the Copenhagen General Population study, 2 similar prospective studies conducted in the Danish general population. Individuals had information on plasma lipoprotein(a) concentrations (n = 59980), LPA kringle-IV type 2 (KIV-2) number of repeats (n = 98965), and/or LPA single-nucleotide polymorphism rs10455872 associated with high lipoprotein(a) concentrations (n = 109 169), and information on hospital contacts or death due to major bleeding in brain and airways from registers.

RESULTS

Using extreme phenotypes or genotypes, the multifactorially adjusted hazard ratio for major bleeding in the brain and airways was 0.84 (95%CI: 0.71-0.99) for lipoprotein(a), >800 mg/L vs <110 mg/L; 0.83 (0.73-0.96) for KIV-2, <24 vs >35 number of repeats; and 0.89 (0.81-0.97) for rs10455872 carriers (heterozygotes + homozygotes) vs noncarriers. The corresponding hazard ratios were 0.89 (0.82-0.98) for heterozygotes and 0.59 (0.36-0.98) for homozygotes separately vs rs10455872 noncarriers. Also, for a 1 standard deviation higher lipoprotein(a) (= 310 mg/L), the hazard ratio for major bleeding in the brain and airways was 0.95 (95%CI: 0.91-1.00) observationally, 0.89 (0.80-0.98) causally based on LPA KIV-2 number of repeats, and 0.94 (0.87-1.02) causally based on LPA rs10455872.

CONCLUSIONS

High lipoprotein(a) concentrations were associated with lower risk of major bleeding in the brain and airways observationally and causally. This indicates that lipoprotein(a) may play a role in hemostasis and wound healing.

Lipoprotein(a) in patients with aortic stenosis: Insights from cardiovascular magnetic resonance

Background

Aortic stenosis is the most common age-related valvular pathology. Patients with aortic stenosis and myocardial fibrosis have worse outcome but the underlying mechanism is unclear. Lipoprotein(a) is associated with adverse cardiovascular risk and is elevated in patients with aortic stenosis. Although mechanistic pathways could link Lipoprotein(a) with myocardial fibrosis, whether the two are related has not been previously explored. In this study, we investigated whether elevated Lipoprotein(a) was associated with the presence of myocardial replacement fibrosis.

Methods

A total of 110 patients with mild, moderate and severe aortic stenosis were assessed by late gadolinium enhancement (LGE) cardiovascular magnetic resonance to identify fibrosis. Mann Whitney U tests were used to assess for evidence of an association between Lp(a) and the presence or absence of myocardial fibrosis and aortic stenosis severity and compared to controls. Univariable and multivariable linear regression analysis were undertaken to identify possible predictors of Lp(a).

Results

Thirty-six patients (32.7%) had no LGE enhancement, 38 (34.6%) had midwall enhancement suggestive of midwall fibrosis and 36 (32.7%) patients had subendocardial myocardial fibrosis, typical of infarction. The aortic stenosis patients had higher Lp(a) values than controls, however, there was no significant difference between the Lp(a) level in mild, moderate or severe aortic stenosis. No association was observed between midwall or infarction pattern fibrosis and Lipoprotein(a), in the mild/moderate stenosis (p = 0.91) or severe stenosis patients (p = 0.42).

Conclusion

There is no evidence to suggest that higher Lipoprotein(a) leads to increased myocardial midwall or infarction pattern fibrosis in patients with aortic stenosis.

Elevated lipoprotein (a) levels are an independent risk factor for retinal vein occlusion

PURPOSE

To investigate the prevalence of lipoprotein (a) [Lp(a)] and other thrombophilic disorders among retinal vein occlusion (RVO) patients with regard to age and various risk factors.

METHODS

We retrospectively reviewed the medical records of 100 patients with central, hemicentral or branch RVO who had undergone routine thrombophilia screening. Data were compared with 100 controls. Both cohorts were divided into three subgroups (≤45 years, >45-≤60 years or >60 years), depending on the patients' age at the time of the RVO or a previous thromboembolic event.

RESULTS

Elevated Lp(a) plasma levels were significantly more prevalent among RVO patients than among controls (p < 0.0001; OR: 4.8). Moreover, we determined age ≤60 years by the time of the first thromboembolic event as a strong predictor of elevated Lp(a) (p = 0.0002). The coincidence of elevated Lp(a) with other coagulation disorders further increased the OR for RVO to 9.3 (95% CI 2.1-41.8). Multivariate analysis revealed the presence of cardiovascular risk factors (OR: 3.1, p = 0.0004), elevated lipoprotein (a) levels (OR: 5.2, p = 0.0001) and increased factor VIII activity (OR: 5.9, p = 0.001) as independent risk factors for the development of RVO among patients.

CONCLUSION

Our results indicate that elevated plasma levels of Lp(a) are associated with the development of RVO. Selective screening of young patients and subjects with a personal or family history of thromboembolism may be helpful in identifying RVO patients with elevated Lp(a).

Fibrin Formation, Structure and Properties

Fibrinogen and fibrin are essential for hemostasis and are major factors in thrombosis, wound healing, and several other biological functions and pathological conditions. The X-ray crystallographic structure of major parts of fibrin(ogen), together with computational reconstructions of missing portions and numerous biochemical and biophysical studies, have provided a wealth of data to interpret molecular mechanisms of fibrin formation, its organization, and properties. On cleavage of fibrinopeptides by thrombin, fibrinogen is converted to fibrin monomers, which interact via knobs exposed by fibrinopeptide removal in the central region, with holes always exposed at the ends of the molecules. The resulting half-staggered, double-stranded oligomers lengthen into protofibrils, which aggregate laterally to make fibers, which then branch to yield a three-dimensional network. Much is now known about the structural origins of clot mechanical properties, including changes in fiber orientation, stretching and buckling, and forced unfolding of molecular domains. Studies of congenital fibrinogen variants and post-translational modifications have increased our understanding of the structure and functions of fibrin(ogen). The fibrinolytic system, with the zymogen plasminogen binding to fibrin together with tissue-type plasminogen activator to promote activation to the active proteolytic enzyme, plasmin, results in digestion of fibrin at specific lysine residues. In spite of a great increase in our knowledge of all these interconnected processes, much about the molecular mechanisms of the biological functions of fibrin(ogen) remains unknown, including some basic aspects of clotting, fibrinolysis, and molecular origins of fibrin mechanical properties. Even less is known concerning more complex (patho)physiological implications of fibrinogen and fibrin.

Effect of Two Lipoprotein (a)-Associated Genetic Variants on Plasminogen Levels and Fibrinolysis

Two genetic variants (rs3798220 and rs10455872) in the apolipoprotein (a) gene (LPA) have been implicated in cardiovascular disease (CVD), presumably through their association with lipoprotein (a) [Lp(a)] levels. While Lp(a) is recognized as a lipoprotein with atherogenic and thrombogenic characteristics, it is unclear whether or not the two Lp(a)-associated genetic variants are also associated with markers of thrombosis (i.e., plasminogen levels and fibrinolysis). In the present study, we genotyped the two genetic variants in 2919 subjects of the Old Order Amish (OOA) and recruited 146 subjects according to the carrier and noncarrier status for rs3798220 and rs10455872, and also matched for gender and age. We measured plasma Lp(a) and plasminogen levels in these subjects, and found that the concentrations of plasma Lp(a) were 2.62- and 1.73-fold higher in minor allele carriers of rs3798220 and rs10455872, respectively, compared with noncarriers (P = 2.04 × 10⁻¹⁷ and P = 1.64 × 10⁻⁶, respectively). By contrast, there was no difference in plasminogen concentrations between carriers and noncarriers of rs3798220 and rs10455872. Furthermore, we observed no association between carrier status of rs3798220 or rs10455872 with clot lysis time. Finally, plasminogen mRNA expression in liver samples derived from 76 Caucasian subjects was not significantly different between carriers and noncarriers of these two genetic variants. Our results provide further insight into the mechanism of action behind two genetic variants previously implicated in CVD risk and show that these polymorphisms are not major modulating factors for plasma plasminogen levels and fibrinolysis.

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

Lipoprotein (a): truly a direct prothrombotic factor in cardiovascular disease?

Elevated plasma concentrations of lipoprotein (a) [Lp(a)] have been determined to be a causal risk factor for coronary heart disease, and may similarly play a role in other atherothrombotic disorders. Lp(a) consists of a lipoprotein moiety indistinguishable from LDL, as well as the plasminogen-related glycoprotein, apo(a). Therefore, the pathogenic role for Lp(a) has traditionally been considered to reflect a dual function of its similarity to LDL, causing atherosclerosis, and its similarity to plasminogen, causing thrombosis through inhibition of fibrinolysis. This postulate remains highly speculative, however, because it has been difficult to separate the prothrombotic/antifibrinolytic functions of Lp(a) from its proatherosclerotic functions. This review surveys the current landscape surrounding these issues: the biochemical basis for procoagulant and antifibrinolytic effects of Lp(a) is summarized and the evidence addressing the role of Lp(a) in both arterial and venous thrombosis is discussed. While elevated Lp(a) appears to be primarily predisposing to thrombotic events in the arterial tree, the fact that most of these are precipitated by underlying atherosclerosis continues to confound our understanding of the true pathogenic roles of Lp(a) and, therefore, the most appropriate therapeutic target through which to mitigate the harmful effects of this lipoprotein.

A comparative study on serum lipoprotein (a) and lipid profile between rheumatoid arthritis patients and normal subjects

BACKGROUND

Rheumatoid arthritis is a chronic and systemic inflammatory disorder, in which Lipoprotein (a) [Lp (a)] increases plaque formation and thus promotes atherosclerosis. Coronary artery disease is one of the co-morbidity in rheumatoid arthritis patients.

AIM

The aim of this study is to evaluate Lp (a) as a cardiovascular risk factor in patients with rheumatoid arthritis. This was a comparative study in which Lp (a) and lipid profile were compared in rheumatoid arthritis patients and controls.

MATERIALS AND METHODS

The study included 30 sero-positive rheumatoid arthritis patients and 30 normal healthy subjects with an age and sex matched group of 25-80 years. Statistical analysis was performed using SPSS version 17.

RESULTS

Serum Lp (a) concentration was significantly increased (P < 0.001) in rheumatoid arthritis patients compared with controls. Serum high-density lipoprotein-cholesterol was significantly lowered (P < 0.05) in patients as compared to controls. There was no significant difference in serum total cholesterol, triglycerides, and very low density lipoprotein-cholesterol between patients and controls.

CONCLUSION

The findings indicate that the patients with rheumatoid arthritis are at high risk of developing cardiovascular disease in future due to the increased level of Lp (a). In addition to conventional lipid profile, estimation of Lp (a) can prove to be a valuable tool in risk assessment of population in general and management of disease in particular.

A Phase II Multicenter Trial With Rivaroxaban in the Treatment of Livedoid Vasculopathy Assessing Pain on a Visual Analog Scale

BACKGROUND

Livedoid vasculopathy is an orphan skin disease characterized by recurrent thrombosis of the cutaneous microcirculation. It manifests itself almost exclusively in the ankles, the back of the feet, and the distal part of the lower legs. Because of the vascular occlusion, patients suffer from intense local ischemic pain. Incidence of livedoid vasculopathy is estimated to be around 1:100,000. There are currently no approved treatments for livedoid vasculopathy, making off-label therapy the only option. In Europe, thromboprophylactic treatment with low-molecular-weight heparins has become widely accepted.

OBJECTIVE

The aim of this trial is the statistical verification of the therapeutic effects of the anticoagulant rivaroxaban in patients suffering from livedoid vasculopathy.

METHODS

We performed a therapeutic phase IIa trial designed as a prospective, one-armed, multicenter, interventional series of cases with a calculated sample size of 20 patients. The primary outcome is the assessment of local pain on the visual analog scale (VAS) as an intraindividual difference of 2 values between baseline and 12 weeks.

RESULTS

Enrollment started in December 2012 and was still open at the date of submission. The study is expected to finish in November 2014.

CONCLUSIONS

Livedoid vasculopathy is associated with increased thrombophilia in the cutaneous microcirculation and the continuous use of anticoagulants helps improve the symptoms. The causes of cutaneous infarctions are heterogenous, but ultimately follow the known mechanisms of the coagulation cascade. Rivaroxaban affects the coagulation cascade and inhibits the factor Xa-dependent conversion of prothrombin to thrombin, thereby considerably reducing the risk of thrombosis.

TRIAL REGISTRATION

Trial Registration EudraCT Number: 2012-000108-13-DE; https://www.clinicaltrialsregister.eu/ctr-search/search?query=eudract_number:2012-000108-13 (Archived by WebCite at http://www.webcitation.org/6UCktWVCA); German Clinical Trials Register (DRKS): DRKS00004652; https://drks-neu.uniklinik-freiburg.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00004652 (Archived by WebCite at http://www.webcitation.org/6UCIAKyCS).

Lipoprotein(a): an important cardiovascular risk factor and a clinical conundrum

Elevated plasma concentrations of lipoprotein(a) (Lp[a]) are an emerging risk factor for the development of coronary heart disease (CHD). Recent genetic and epidemiologic data have provided strong evidence for a causal role of Lp(a) in CHD. Despite these developments, which have attracted increasing interest from clinicians and basic scientists, many unanswered questions persist. The true pathogenic mechanism of Lp(a) remains a mystery. Significant uncertainty exists concerning the appropriate use of Lp(a) in the clinical setting. No therapeutic intervention remains that can specifically lower plasma Lp(a) concentrations, although the list of compounds that lower Lp(a) and LDL continues to expand.

Elevated lipoprotein(a) in a newborn with thrombosis and a family history of dyslipidemia

This paper reports a rare case of elevated lipoproteinemia(a) that evolved into thrombosis during the neonatal period. During the first days of life, the patient presented with an intracardiac thrombus, pulmonary thromboembolism and a hemorrhagic stroke. Initially, the results of the blood tests performed to screen for thrombophilic diseases were normal for the patient's age. The maternal dyslipidemia and the family's positive history of thromboembolism drew attention to an underlying, inherited, thrombophilic defect. Upon further investigation of the thrombophilia, the increase in lipoprotein(a) levels found in the mother and infant enabled the diagnosis of hyperlipoprotein(a) and the administration of appropriate therapy.

Lp(a) is not associated with diabetes but affects fibrinolysis and clot structure ex vivo

Lipoprotein (a) [Lp(a)] is a low density lipoprotein (LDL) with one apolipoprotein (a) molecule bound to the apolipoprotein B-100 of LDL. Lp(a) is an independent risk factor for cardiovascular disease (CVD). However, the relationship of Lp(a) to diabetes and metabolic syndrome, both known for increased CVD risk, is controversial. In a population based study on type two diabetes mellitus (T2DM) development in women, Lp(a) plasma levels showed the well known skewed distribution without any relation to diabetes or impaired glucose tolerance. A modified clot lysis assay on a subset of 274 subjects showed significantly increased clot lysis times in T2DM subjects, despite inhibition of PAI-1 and TAFI. Lp(a) plasma levels significantly increased the maximal peak height of the clot lysis curve, indicating a change in clot structure. In this study Lp(a) is not related to the development of T2DM but may affect clot structure ex vivo without a prolongation of the clot lysis time.

Inhibition of plasminogen activation by apo(a): role of carboxyl-terminal lysines and identification of inhibitory domains in apo(a)

Apo(a), the distinguishing protein component of lipoprotein(a) [Lp(a)], exhibits sequence similarity to plasminogen and can inhibit binding of plasminogen to cell surfaces. Plasmin generated on the surface of vascular cells plays a role in cell migration and proliferation, two of the fibroproliferative inflammatory events that underlie atherosclerosis. The ability of apo(a) to inhibit pericellular plasminogen activation on vascular cells was therefore evaluated. Two isoforms of apo(a), 12K and 17K, were found to significantly decrease tissue-type plasminogen activator-mediated plasminogen activation on human umbilical vein endothelial cells (HUVECs) and THP-1 monocytes and macrophages. Lp(a) purified from human plasma decreased plasminogen activation on THP-1 monocytes and HUVECs but not on THP-1 macrophages. Removal of kringle V or the strong lysine binding site in kringle IV10 completely abolished the inhibitory effect of apo(a). Treatment with carboxypeptidase B to assess the roles of carboxyl-terminal lysines in cellular receptors leads in most cases to decreases in plasminogen activation as well as plasminogen and apo(a) binding; however, inhibition of plasminogen activation by apo(a) was unaffected. Our findings directly demonstrate that apo(a) inhibits pericellular plasminogen activation in all three cell types, although binding of apo(a) to cell-surface receptors containing carboxyl-terminal lysines does not appear to play a major role in the inhibition mechanism.

Lipoprotein (a), LPA Ile4399Met, and fibrin clot properties

INTRODUCTION

Elevated lipoprotein(a) (Lp(a)) levels were reported to be associated with dense fibrin clots. The apo(a) component of Lp(a) is encoded by LPA, and the Met allele of the LPA Ile4399Met polymorphism is associated with elevated Lp(a) levels and cardiovascular disease risk. We investigated whether Ile4399Met was associated with fibrin clot properties.

MATERIALS AND METHODS

We determined plasma Lp(a) levels, fibrin clot permeability and lysis time for 64 LPA 4399Met carriers and 128 noncarriers matched for age, sex, ethnicity, and enrollment site.

RESULTS

Elevated Lp(a) levels were associated with reduced clot permeability and prolonged lysis time (P<0.0001). Carriers of 4399Met had higher Lp(a) levels compared with noncarriers (P=0.0003). However, this association differed by ethnicity (P=0.003 for interaction between genotype and ethnicity): compared with noncarriers, 4399Met carriers had 2.89 fold higher Lp(a) levels among Caucasians while no difference was observed among non-Caucasians (primarily East Asians and Hispanics). Among all subjects, no association was observed between Ile4399Met and clot properties, but this relationship also differed by ethnicity: among non-Caucasians, 4399Met carriers had increased clot permeability and shorter lysis time; whereas among Caucasians, the trend was for decreased permeability and longer lysis time (P<0.01 for interactions between genotype and ethnicity).

CONCLUSIONS

We confirmed that elevated Lp(a) levels are associated with dense fibrin clots, and found that the association of LPA 4399Met carriers and clot permeability as well as lysis time differ by ethnicity.

High-throughput proteomic characterization of plasma rich in growth factors (PRGF-Endoret)-derived fibrin clot interactome

Plasma rich in growth factors (PRGF®-Endoret®) is an autologous technology that contains a set of proteins specifically addressed to wound healing and tissue regeneration. The scaffold formed by using this technology is a clot mainly composed of fibrin protein, forming a three-dimensional (3D) macroscopic network. This biomaterial is easily obtained by biotechnological means from blood and can be used in a range of situations to help wound healing and tissue regeneration. Although the main constituent of this clot is the fibrin scaffold, little is known about other proteins interacting in this clot that may act as adjuvants in the healing process. The aim of this study was to characterize the proteins enclosed by PRGF-Endoret scaffold, using a double-proteomic approach that combines 1D-SDS-PAGE approach followed by LC-MS/MS, and 2-DE followed by MALDI-TOF/TOF. The results presented here provide a description of the catalogue of key proteins in close contact with the fibrin scaffold. The obtained lists of proteins were grouped into families and networks according to gene ontology. Taken together, an enrichment of both proteins and protein families specifically involved in tissue regeneration and wound healing has been found.

Livedoid vasculopathy: an intringuing cutaneous disease

Livedoid vasculopathy is a skin disease that occludes the blood vessels of the dermis. It has a pauciinflammatory or non-inflammatory nature. It is characterized by the presence of macular or papular, erythematous-purpuric lesions affecting the legs, especially the ankles and feet, and producing intensely painful ulcerations, which cause white atrophic scars called "atrophie blanche". This review includes studies and case reports found in the medical literature regarding the etiopathogenic associations of the disease, particularly those related to thrombophilia, their histopathological findings and the therapeutic approaches used in the difficult clinical management of these cases.

Identification of fibrin clot-bound plasma proteins

Several proteins are known to bind to a fibrin network and to change clot properties or function. In this study we aimed to get an overview of fibrin clot-bound plasma proteins. A plasma clot was formed by adding thrombin, CaCl₂ and aprotinin to citrated platelet-poor plasma and unbound proteins were washed away with Tris-buffered saline. Non-covalently bound proteins were extracted, separated with 2D gel electrophoresis and visualized with Sypro Ruby. Excised protein spots were analyzed with mass spectrometry. The identity of the proteins was verified by checking the mass of the protein, and, if necessary, by Western blot analysis. Next to established fibrin-binding proteins we identified several novel fibrin clot-bound plasma proteins, including α₂-macroglobulin, carboxypeptidase N, α₁-antitrypsin, haptoglobin, serum amyloid P, and the apolipoproteins A-I, E, J, and A-IV. The latter six proteins are associated with high-density lipoprotein particles. In addition we showed that high-density lipoprotein associated proteins were also present in fibrinogen preparations purified from plasma. Most plasma proteins in a fibrin clot can be classified into three groups according to either blood coagulation, protease inhibition or high-density lipoprotein metabolism. The presence of high-density lipoprotein in clots might point to a role in hemostasis.

Features of two proteins of Leptospira interrogans with potential role in host-pathogen interactions

Background

Leptospirosis is considered a re-emerging infectious disease caused by pathogenic spirochaetes of the genus Leptospira. Pathogenic leptospires have the ability to survive and disseminate to multiple organs after penetrating the host. Leptospires were shown to express surface proteins that interact with the extracellular matrix (ECM) and to plasminogen (PLG). This study examined the interaction of two putative leptospiral proteins with laminin, collagen Type I, collagen Type IV, cellular fibronectin, plasma fibronectin, PLG, factor H and C4bp.

Results

We show that two leptospiral proteins encoded by LIC11834 and LIC12253 genes interact with laminin in a dose - dependent and saturable mode, with dissociation equilibrium constants (K_D) of 367.5 and 415.4 nM, respectively. These proteins were named Lsa33 and Lsa25 (Leptospiral surface adhesin) for LIC11834 and LIC12253, respectively. Metaperiodate - treated laminin reduced Lsa25 - laminin interaction, suggesting that sugar moieties of this ligand participate in this interaction. The Lsa33 is also PLG - binding receptor, with a K_D of 23.53 nM, capable of generating plasmin in the presence of an activator. Although in a weak manner, both proteins interact with C4bp, a regulator of complement classical route. In silico analysis together with proteinase K and immunoflorescence data suggest that these proteins might be surface exposed. Moreover, the recombinant proteins partially inhibited leptospiral adherence to immobilized laminin and PLG.

Conclusions

We believe that these multifunctional proteins have the potential to participate in the interaction of leptospires to hosts by mediating adhesion and by helping the bacteria to escape the immune system and to overcome tissue barriers. To our knowledge, Lsa33 is the first leptospiral protein described to date with the capability of binding laminin, PLG and C4bp in vitro.

The effect of thyroid disorders on lipid levels and metabolism

Thyroid hormones regulate cholesterol and lipoprotein metabolism, whereas thyroid disorders, including overt and subclinical hypothyroidism, considerably alter lipid profile and promote cardiovascular disease. Good evidence shows that high thyroid-stimulating hormone (TSH) is associated with a nonfavorable lipid profile, although TSH has no cutoff threshold for its association with lipids. Thyromimetics represent a new class of hypolipidemic drugs: their imminent application in patients with severe dyslipidemias, combined or not with statins, will improve the lipid profile, potentially accelerate energy expenditure and, as a consequence, vitally lessen the risk of cardiovascular disease.

Fibrinogen, Lp(a), Microalbuminuria and Left Ventricular Mass Index: Cardiovascular Disease Risk factors in Diabetes

The present work was undertaken to study interrelation of Fibrinogen, Lp(a) and LVMI in Type II diabetes patients with or without nephropathy. 100 Type II Diabetic patients attending OPD/IPD of DMC&H, Ludhiana were included. They were divided in two groups. Group I: 50 patients without microalbuminuria (MAU). Group II: 50 patients with MAU. Fibrinogen (Clauss method), Lp(a) and MAU were estimated on Multichannel Autoanalyzer Hitachi-911 (Roche). LVMI was estimated by echocardiography using formula of Devereux and Reicheck. Type II diabetes patients with MAU had significantly raised levels of Fibrinogen, Lp(a), and LVMI as compared to normoalbuminuric diabetics (P < 0.01). Group II patients had positive correlation between Lp(a) and LVMI but no relation between Fibrinogen and LVMI. MAU, marker of microangiopathy, is associated with higher Fibrinogen and Lp(a) levels. This becomes basis of increase cardiovascular risk as demonstrated by higher mean LVMI in Group II patients.

Bleeding and thrombotic complications of kidney disease

With the rising prevalence of kidney disease, clinicians are increasingly faced with concerns about potential thrombotic and bleeding complications. Thrombotic risk, both arterial and venous, predominates with all severities of kidney disease but bleeding manifestations become an additional concern particularly with uraemia. This article reviews these contrasting problems and discusses strategies for prevention and management in the context of renal impairment, renal replacement therapy and renal transplantation.

The novel leptospiral surface adhesin Lsa20 binds laminin and human plasminogen and is probably expressed during infection

Leptospirosis is an emerging infectious disease caused by pathogenic species of Leptospira. In this work, we report the cloning, expression, purification, and characterization of two predicted leptospiral outer membrane proteins, LIC11469 and LIC11030. The LIC11469 protein is well conserved among leptospiral strains, while LIC11030 was identified only in Leptospira interrogans. We confirmed by surface proteolysis of intact leptospires with proteinase K that these proteins are most likely new surface leptospiral proteins. The recombinant proteins were evaluated for their capacity to attach to extracellular matrix (ECM) components and to plasminogen. The leptospiral protein encoded by LIC11469, named Lsa20 (leptospiral surface adhesin of 20 kDa), binds to laminin and to plasminogen. The binding with both components was not detected when Lsa20 was previously denatured or blocked with anti-Lsa20 antibodies. Moreover, Lsa20 binding to laminin was also confirmed by surface plasmon resonance (SPR). Laminin competes with plasminogen for binding to Lsa20, suggesting the same ligand-binding site. Lsa20-bound plasminogen could be converted to enzymatically active plasmin, capable of cleaving plasmin substrate d-valyl-leucyl-lysine-p-nitroanilide dihydrochloride. Lsa20 was recognized by antibodies in confirmed-leptospirosis serum samples, suggesting that this protein is expressed during infection. Taken together, our results indicate that Lsa20 is a novel leptospiral adhesin that in concert with the host-derived plasmin may help the bacteria to adhere and to spread through the hosts.

Increased stroke risk and lipoprotein(a) in a multiethnic community: the Northern Manhattan Stroke Study

CONTEXT

Elevated lipoprotein(a) [Lp(a)] is associated with ischemic stroke (IS) among Whites, but data is sparse for non-White populations.

OBJECTIVE

Using a population-based case-control study design with subjects from the Northern Manhattan Stroke Study, we assessed whether Lp(a) levels were independently associated with IS risk among Whites, Blacks and Hispanics.

DESIGN AND SETTING

Lp(a) levels were measured in 317 IS cases (mean age 69 +/- 13 years; 56% women; 16% Whites, 31% Blacks and 52% Hispanics) and 413 community-based controls, matched by age, race/ethnicity and gender. In-person assessments included demographics, socioeconomic status, presence of vascular risk factors and fasting lipid levels. Logistic regression was used to determine the independent association of Lp(a) and IS. Stratified analyses investigated gender and race/ethnic differences.

RESULTS

Mean Lp(a) levels were greater among cases than controls (46.3 +/- 41.0 vs. 38.9 +/- 38.2 mg/dl; p < 0.01). After adjusting for stroke risk factors (hypertension, diabetes mellitus, coronary artery disease, cigarette smoking), lipid levels, and socioeconomic status, Lp(a) levels > or =30 mg/dl were independently associated with an increased stroke risk in the overall cohort (adjusted odds ratio, OR, 1.8, 95% confidence interval, CI, 1.20-2.6; p = 0.004). There was a significant linear dose-response relationship between Lp(a) levels and IS risk. The association between IS risk and Lp(a) > or =30 mg/dl was more pronounced among men (adjusted OR 2.0, 95% CI 1.1-3.5; p = 0.02) and among Blacks (adjusted OR 2.7, 95% CI 1.2-6.2; p = 0.02).

CONCLUSION

Elevated Lp(a) levels were significantly and independently associated with increased stroke risk, suggesting that Lp(a) is a risk factor for IS across White, Black and Hispanic race/ethnic groups.

Association of Apo(a)isoform size with dyslipoproteinemia in male venous thrombosis patients

BACKGROUND

Lp(a) is a proatherogenic lipoprotein that may also be prothrombotic. Apo(a) size isoforms have differential effects on fibrinolysis. Whereas Lp(a) concentrations have been linked to venous thromboembolic disease (VTE) risk, apo(a) polymorphisms in VTE have not been studied.

METHODS

We used a standardized high resolution agarose gel electrophoresis technique to determine apo(a) isoform size, and a Lp(a) immunoassay insensitive to apo(a) size to measure Lp(a) concentration in 46 men with VTE and 46 age-matched healthy controls.

RESULTS

Apo(a) isoform distribution in VTE cases and controls was bimodal and VTE patients tended to have more medium-sized isoforms K(4)-(19-27) (54.3% vs. 34.8%, p=0.06). Cases and controls had the same median predominant apo(a) size isoform (23.5 K(4) repeats) and comparable Lp(a) concentrations. However, subgroup analysis based on apo(a) isoform size (K(4)< or =23 or K(4)> or =24) revealed that cases in the K(4)> or =24 subgroup had higher Lp(a) concentrations than the controls in this isofrom subgroup (14.5 mmol vs. 6.6 mmol, p=0.029). Also, dyslipoproteinemia (smaller LDL and HDL particles, higher LDL and lower HDL parameters) was strongly associated with VTE only in this larger apo(a) isoform group.

CONCLUSIONS

These observations provide the first evidence that determination of apo(a) isoforms may provide useful novel insights into VTE risk.

Plasminogen on the surfaces of fibrin clots prevents adhesion of leukocytes and platelets

BACKGROUND AND OBJECTIVES

Although leukocytes and platelets adhere to fibrin with alacrity in vitro, these cells do not readily accumulate on the surfaces of fibrin clots in vivo. The difference in the capacity of blood cell integrins to adhere to fibrin in vivo and in vitro is striking and implies the existence of a physiologic antiadhesive mechanism. The surfaces of fibrin clots in the circulation are continually exposed to plasma proteins, several of which can bind fibrin and influence cell adhesion. Recently, we have demonstrated that adsorption of soluble fibrinogen on the surface of a fibrin clot results in its deposition as a soft multilayer matrix, which prevents attachment of blood cells. In the present study, we demonstrate that another plasma protein, plasminogen, which is known to accumulate in the superficial layer of fibrin, exerts an antiadhesive effect.

RESULTS

After being coated with plasminogen, the surfaces of fibrin clots became essentially non-adhesive for U937 monocytic cells, blood monocytes, and platelets. The data revealed that activation of fibrin-bound plasminogen by the plasminogen-activating system assembled on adherent cells resulted in the generation of plasmin, which decomposed the superficial fibrin layer, resulting in cell detachment under flow. The surfaces generated after the initial cell adhesion remained non-adhesive for subsequent attachment of leukocytes and platelets.

CONCLUSION

We propose that the limited degradation of fibrin by plasmin generated by adherent cells loosens the fibers on the clot surface, producing a mechanically unstable substrate that is unable to support firm integrin-mediated cell adhesion.

Niacin and fibrates in atherogenic dyslipidemia: pharmacotherapy to reduce cardiovascular risk

Although statin therapy represents a cornerstone of cardiovascular disease (CVD) prevention, a major residual CVD risk (60-70% of total relative risk) remains, attributable to both modifiable and non-modifiable risk factors. Among the former, low levels of HDL-C together with elevated triglyceride (TG)-rich lipoproteins and their remnants represent major therapeutic targets. The current pandemic of obesity, metabolic syndrome, and type 2 diabetes is intimately associated with an atherogenic dyslipidemic phenotype featuring low HDL-C combined with elevated TG-rich lipoproteins and small dense LDL. In this context, there is renewed interest in pharmacotherapeutic strategies involving niacin and fibrates in monotherapy and in association with statins. This comprehensive, critical review of available data in dyslipidemic subjects indicates that niacin is more efficacious in raising HDL-C than fibrates, whereas niacin and fibrates reduce TG-rich lipoproteins and LDL comparably. Niacin is distinguished by its unique capacity to effectively lower Lp(a) levels. Several studies have demonstrated anti-atherosclerotic action for both niacin and fibrates. In contrast with statin therapy, the clinical benefit of fibrates appears limited to reduction of nonfatal myocardial infarction, whereas niacin (frequently associated with statins and/or other agents) exerts benefit across a wider range of cardiovascular endpoints in studies involving limited patient numbers. Clearly the future treatment of atherogenic dyslipidemias involving the lipid triad, as exemplified by the occurrence of the mixed dyslipidemic phenotype in metabolic syndrome, type 2 diabetes, renal, and auto-immune diseases, requires integrated pharmacotherapy targeted not only to proatherogenic particles, notably VLDL, IDL, LDL, and Lp(a), but also to atheroprotective HDL.

Identification of quantitative trait loci for fibrin clot phenotypes: the EuroCLOT study

OBJECTIVE

Fibrin makes up the structural basis of an occlusive arterial thrombus, and variability in fibrin phenotype relates to cardiovascular risk. The aims of the current study from the EU consortium EuroCLOT were to (1) determine the heritability of fibrin phenotypes and (2) identify QTLs associated with fibrin phenotypes.

METHODS AND RESULTS

447 dizygotic (DZ) and 460 monozygotic (MZ) pairs of healthy UK white female twins and 199 DZ twin pairs from Denmark were studied. D-dimer, an indicator of fibrin turnover, was measured by ELISA and measures of clot formation, morphology, and lysis were determined by turbidimetric assays. Heritability estimates and genome-wide linkage analysis were performed. Estimates of heritability for d-dimer and turbidometric variables were in the range 17% to 46%, with highest levels for maximal absorbance which provides an estimate of clot density. Genome-wide linkage analysis revealed 6 significant regions with LOD >3 on 5 chromosomes (5, 6, 9, 16, and 17).

CONCLUSIONS

The results indicate a significant genetic contribution to variability in fibrin phenotypes and highlight regions in the human genome which warrant further investigation in relation to ischemic cardiovascular disorders and their therapy.

Apolipoprotein(a) inhibits the conversion of Glu-plasminogen to Lys-plasminogen: a novel mechanism for lipoprotein(a)-mediated inhibition of plasminogen activation

BACKGROUND

Elevated plasma concentrations of lipoprotein(a) [Lp(a)] are associated with an increased risk for thrombotic disorders. Lp(a) is a unique lipoprotein consisting of a low-density lipoprotein-like moiety covalently linked to apolipoprotein(a) [apo(a)], a homologue of the fibrinolytic proenzyme plasminogen. Several in vitro and in vivo studies have shown that Lp(a)/apo(a) can inhibit tissue-type plasminogen activator-mediated plasminogen activation on fibrin surfaces, although the mechanism of inhibition by apo(a) remains controversial. Essential to fibrin clot lysis are a number of plasmin-dependent positive feedback reactions that enhance the efficiency of plasminogen activation, including the plasmin-mediated conversion of Glu-plasminogen to Lys-plasminogen.

OBJECTIVE

Using acid-urea gel electrophoresis to resolve the two forms of radiolabeled plasminogen, we determined whether apo(a) is able to inhibit Glu-plasminogen to Lys-plasminogen conversion.

METHODS

The assays were performed in the absence or presence of different recombinant apo(a) species, including point mutants, deletion mutants and variants that represent greater than 90% of the known apo(a) isoform sizes.

RESULTS

Apo(a) substantially suppressed Glu-plasminogen conversion. Critical roles were identified for the kringle IV types 5-9 and kringle V; contributory roles for sequences within the amino-terminal half of the molecule were also observed. Additionally, with the exception of the smallest naturally-occurring isoform of apo(a), isoform size was found not to contribute to the inhibitory capacity of apo(a).

CONCLUSION

These findings underscore a novel contribution to the understanding of Lp(a)/apo(a)-mediated inhibition of plasminogen activation: the ability of the apo(a) component of Lp(a) to inhibit the key positive feedback step of plasmin-mediated Glu-plasminogen to Lys-plasminogen conversion.

Hypercoagulability markers in patients with peripheral arterial disease: association to ankle-brachial index

Peripheral arterial disease is diagnosed by measuring the ankle-brachial index. Values lower than 0.90 define the disease being usually related to its severity. Patients with peripheral arterial disease may show a hypercoagulability state. The aim of this study was to assess hemostatic variables and to correlate them with the presence of peripheral arterial disease and its severity as assessed by ankle-brachial index values. Plasma levels of D dimer, plasminogen, prothrombin fragment 1+2, plasminogen activator inhibitor and thrombomodulin were measured in 36 patients with peripheral arterial disease (group 1) and 30 without disease (group 2). Significant differences for D dimer, plasminogen, prothrombin fragment 1+2 and plasminogen activator inhibitor type 1 between the 2 groups were found (P<0.05). Significant and inverse correlations were also observed (Pearson correlation, P<0.05) between ankle-brachial index values and levels of both plasminogen and plasminogen activator inhibitor type 1. Although there was no significant correlation between ankle-brachial index and levels of D dimer, higher D dimer values were observed in patients with lower ankle-brachial index values. The results confirm a trend to hypercoagulability and hypofibrinolysis in patients with peripheral arterial disease. Increased levels of plasminogen activator inhibitor type 1 seem to be associated with the severity of the disease, considering the inverse correlation between this inhibitor and ankle-brachial index.